The present invention relates to power actuated devices. More precisely the present invention discloses a simplified locking trigger switch for an electric hand tool.
Hand held power tools commonly have a trigger switch whereby depressing the trigger by a finger causes the tool""s power element to become energized. Power tools operated this way include electric drills, staple guns, saws, sanders among other devices. Various home and kitchen appliances also may have a finger trigger switch. Numerous other devices use some type of trigger switch.
A trigger switch usually must have a biasing means to return the switch to its initial condition. A user""s finger acts against this biasing means. An option to lock the trigger against being depressed may also be required, especially when safety is a factor in the operation of the device.
In the case of electric power hand tools the trigger often moves in a linear motion within straight guides of the tool housing. A metal spring presses the switch toward an extended position. In the case of an electric staple or nail gun a trigger lock is typically provided. The common design of this lock includes a plastic bar which may be moved from side to side in the region of the housing where the tool is gripped by a user""s hand. Pressing the lock bar from one side moves the bar to engage the trigger. The switch cannot be moved and the tool cannot be fired. Pressing the lock bar from the other side frees the trigger to engage the switch.
The typical lock bar is a separate part of the trigger assembly. It is difficult to use since it is often engaged or disengaged accidentally as the tool is grasped by a hand. It is also not intuitive which direction to press the lock bar. One must either read the printed information adjacent to the lock bar on the housing, when such information is provided, or try to operate the trigger to find whether the lock is engaged. Naturally it is less safe when the condition of the trigger lock is not immediately obvious.
In the present invention an improved trigger mechanism is disclosed. The trigger is directed to application in a staple or nail gun. However other power actuated devices may also benefit from the trigger of the present invention.
A plastic trigger is rotatably mounted in a tool body. Compared to a linear sliding trigger a rotating trigger operates with less friction since the rotating trigger contacts the housing body slidably only in a gentle guiding action. A linear motion trigger will move with friction that strongly depends on how the finger pressure is applied, with a low friction condition being only when the trigger is pressed directly in the direction of motion. However it is possible to include the features of the present invention in a linear motion trigger with the same benefits described herein for the preferred embodiment rotating trigger.
In the present invention the separate metal reset spring of the prior art is replaced by an extended resilient reset arm of the trigger. Especially when combined with a low friction rotatable trigger, the resilient arm provides an efficient reset action without the use of an additional part.
A further improvement of the invention comprises a locking tab. Being a second resilient extension of the trigger body, the locking tab has a distal end that is normally spaced apart from the trigger body. Moving the tab toward the trigger body causes an element of the tab to prevent the trigger from being depressed. The tab is pulled away from the trigger to disengage the lock.
The locking tab of the present invention is more intuitive than the prior art locking devices since the condition of the tab is visually obvious. When locked the tab is touching the trigger body, when it is unlocked the tab is separate from the trigger body. Importantly the locking tab is not affected by grasping the tool since it is not in an area that is prone to accidental contact.
In the unlocked condition the locking tab moves along with the trigger when the trigger is pressed. In the locked condition the locking tab is restrained against a surface of the tool body.
A feature of the present invention is that three separate functions can be served using a single molded device. Specifically a reset spring and a trigger lock are molded as part of a trigger body.